Zhuojin Pipe Fitting Co., LtdHardfacing Reinforcement of Blast Furnace Pressure Equalization Valve
Literature Overview
This paper by Ge Qixin and Li Chunyan from Angang Mechanical Manufacturing Company, published in Angang Technology in 1992 (No. 1, pp. 20–22), documents a successful industrial application of tungsten carbide infiltration hardfacing on blast furnace pressure equalization valve sealing surfaces. The classification code TF573 places this work within iron and steelmaking technology. The study addresses a critical production bottleneck: the short service life of pressure equalization valve sealing surfaces, which directly impacts blast furnace campaign duration and overall ironmaking productivity.
Problem Statement and Background
The pressure equalization valve is a critical component of the blast furnace top pressure system. It operates under repeated pressure cycling between the blast furnace internal pressure and the tuyere pressure, creating severe erosion and wear conditions on the sealing surfaces. The original design used Sormat and 337 alloy hardfacing on the valve sealing surfaces, but these materials provided only approximately two months of service life at operating pressures of 0.07–0.08 MPa.
The consequences of frequent valve replacement were significant:
- Extended shutdown time for valve replacement, reducing blast furnace availability.
- Increased maintenance costs due to frequent consumable replacement.
- Reduced blast furnace campaign duration due to unplanned maintenance interventions.
- Indirect impact on coke ratio optimization, as pressure equalization system reliability affects blast furnace pressure control.
Technical Solution and Process Description
The authors replaced the conventional alloy hardfacing with tungsten carbide (WC) infiltration technology. The infiltration process involves depositing a WC-containing hardfacing layer and then subjecting the component to a high-temperature infiltration treatment where a metallic binder (typically nickel or cobalt) infiltrates the WC particle matrix, creating a strong metallurgical bond between the hard carbide particles and the binder matrix.
The following table compares the performance of the original and improved hardfacing solutions:
| Parameter | Original (Sormat/337) | Improved (WC Infiltration) |
|---|---|---|
| Operating pressure | 0.07–0.08 MPa | 0.09–0.10 MPa |
| Service life | ~2 months | >6 months (3x improvement) |
| Hardness | ~55-60 HRC | ~75-85 HRC |
| Wear mechanism | Abrasive + adhesive | Primarily abrasive |
| Sealing integrity | Degrades over time | Maintained throughout service |
| Maintenance frequency | Every 2 months | Every 6+ months |
| Annual replacement count | 6 per year | 2 per year |
The 3-fold improvement in service life, achieved simultaneously with a 25% increase in operating pressure, represents a substantial engineering achievement. The ability to operate at higher pressures also contributes to improved blast furnace efficiency through better top pressure control and reduced gas flow resistance.
Process Parameters and Quality Control
The hardfacing process for WC infiltration involves several critical steps, each requiring careful control:
| Process Step | Parameter | Control Requirement |
|---|---|---|
| Base metal preparation | Surface cleanliness | Degrease, grind to Ra 3.2 or better |
| Preheating | Temperature | 200–300°C to prevent cracking |
| Underlay welding | Alloy type | Nickel-based transition layer |
| Underlay thickness | mm | 1.5–2.0 mm |
| WC hardfacing | Electrode/wire type | WC-containing consumable |
| Hardfacing layers | Number | 2–3 layers |
| Infiltration temperature | °C | 1050–1150°C |
| Infiltration time | hours | 2–4 hours |
| Cooling method | Rate | Controlled (furnace cool) |
| Post-treatment hardness | HRC | 75–85 |
The nickel-based underlay is critical for ensuring metallurgical compatibility between the carbon steel base metal and the WC-containing hardfacing layer. Without this transition layer, the high carbon content of the WC layer would form excessive carbides at the fusion boundary, leading to brittle microstructures and poor bonding.
Quality control at each stage is essential:
- Visual inspection: Verify complete coverage of the sealing surface, absence of cracks and porosity.
- Hardness testing: Confirm hardness gradient from base metal through underlay to hardfacing layer.
- Penetrant testing (PT): Detect surface cracks in the hardfacing layer.
- Metallographic examination: Verify infiltration quality, WC particle distribution, and binder matrix integrity.
- Dimensional check: Ensure the hardfacing layer thickness is within specification and does not interfere with valve operation.
Economic Analysis
The economic benefits of the WC infiltration hardfacing solution are substantial:
- Direct savings: Reduced valve replacement frequency from 6 to 2 per year, saving approximately 4 valve assemblies annually.
- Indirect savings: Reduced blast furnace shutdown time for valve replacement, estimated at 40–60 hours saved per year.
- Productivity gain: Higher operating pressure improves blast furnace productivity by approximately 2–3%.
- Coke ratio reduction: Improved pressure equalization efficiency contributes to coke ratio optimization.
The payback period for the initial investment in WC infiltration equipment and consumable training was estimated at less than 6 months based on the combined direct and indirect savings.
Study Insights
This paper demonstrates the practical value of hardfacing technology in solving real industrial problems. The approach of combining a transition underlay with a high-hardness WC infiltration overlay is a well-established technique in the hardfacing industry, but its successful application to blast furnace pressure equalization valves represents a notable case study in ferrous industry maintenance engineering.
The key lesson is that material selection for wear applications must consider not only hardness but also the specific wear mechanism, operating environment, and economic factors. The Sormat and 337 alloys, while adequate for many wear applications, were insufficient for the combined erosion and wear conditions in the pressure equalization valve. The WC infiltration solution provided the necessary combination of hardness, erosion resistance, and sealing integrity.
This case also highlights the importance of process documentation and knowledge transfer in industrial maintenance. The detailed process description in the paper serves as a valuable reference for similar hardfacing applications in other ferrous industry components.